Process for producing an improved cutting tool

ABSTRACT

THE SHARPENED EDGE OF A CUTTING IMPLEMENT SUCH AS A RAZOR BLADE IS MODIFIED BY DEPOSITING A LAYER OF DIELECTRIC MATERIAL ON THE CUTTING EDGE AND THEN DEPOSITING A LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL ON THE DIELECTRIC LAYER AND THEN SUBJECTING THE CUTTING EDGE TO DC ION BOMBARD-   MENT SO THAT A PORTION OF THE DEPOSITED ELECTRICALLY CONDUCTIVE MATERIAL IS REMOVED AND THE DIELECTRIC MATERIAL IS EXPOSED AT THE TIP OF THE IMPLEMENT.

Sept. 25, 1973 A. s. SASTRI 3,761,373

PROCESS FOR PRODUCING AN IMPROVED CUTTING TOOL v Filed July 9, 1971 HG/34.

I -1 1 E '1 z J [4 L ll' Q United States Patent 3,761,373 PROCESS FORPRODUCING AN IMPROVED CUTTING TOOL Aiyaswami S. Sastri, Stow, Mass.,assiguor to The Gillette Company, Boston, Mass. Filed July 9, 1971, Ser.No. 161,159 Int. Cl. B26b 21/54; C23c 15/ 00 U.S. Cl. 204-192 12 ClaimsABSTRACT OF THE DISCLOSURE SUMMARY OF THE INVENTION This inventionrelates to processes for producing an extremely sharp and durablecutting edge on a razor blade or similar cutting tool, and to improvedcutting tools.

The forming of the cutting edges of razor blades by mass productiontechniques conventionally involves a series of abrading operations(grinding and honing) to produce the desired sharpand durable shavingedge. Each abrading operation forms a facet on the blade edge beingsharpened, which facet is modified by subsequent abrading operations ofincreasing fineness. In general, the blade edge configuration is a Wedgeshape, the included solid angle of which is typically 20-30. The facesor sides of such cutting edges may extend back from the ultimate edge adistance up to as much as 0.1 inch or even more. Each face need not be asingle uninterrupted continuous surface or facet, but may consist of twoor more facets formed by successive grinding or honing operations andintersecting each other along zones generally parallel to the ultimateedge. The final facet, i.e. the facet immediately adjacent the ultimateedge, has a width as low as 7.5 microns or even less compared with thediameter of beard hair which averages about 100 to 125 microns. Throughshave test evaluation and measurement of the geometry of such sharpenedcutting edges, it has been found that the cutting edge should have anaverage tip radius of less than 500 Angstroms. A thin adherent layer ofa corrosion resistant metal is often applied to the cutting edge of theblade. Further, a shave facilitating layer of polymeric material is alsofrequently applied to the blade edge. These layers must have adhesioncompatibility so that they remain firmly adhered to one another and tothe substrate throughout the life of the cutting tool and not adverselyaffect the edge geometry.

It is a general object of this invention to provide novel and improvedcutting implements, the cutting edges of which have improved mechanicalproperties.

Another object of the invention is to provide novel and improvedprocesses for producing improved cutting tools.

A further object of the invention is to provide novel and improved razorblades which possess superior shaving properties.

In accordance with the invention, the edge geometry of a cuttingimplement such as a razor blade is modified by a process which includesthe steps of forming a cutting edge of dielectric material, depositing alayer of electrically conductive material on said dielectric material,and then subjecting the composite cutting edge to a DC ion bombardmentstep so that a portion of the deposited 3,761,373 Patented Sept. 25,1973 ice electrically conductive material is removed so that thedielectric material is exposed at the ultimate tip.

In particular embodiments, the cutting edge is formed in a metalsubstrate by a suitable procedure such as grinding, honing, strapping,chemical etching, electrolytic sharpening, or forming with anappropriately shaped die; and then the edge is subjected to twosuccessive strengthening material deposition steps, the first stepdepositing a layer of dielectric material and the second step depositingthe layer of electrically conductive material. Preferably the layers aredeposited by sputtering on a multiplicity of blade elements while theblade edges are disposed in parallel alignment with one another and in aplane parallel to a target member spaced from the blade edges. A planartarget member is used in one embodiment while a cylindrical target rodis used in another embodiment.

A razor blade in accordance with the invention has an average tip radiusof less than 500 Angstroms, the exposed tip material is a dielectric,such as A1 0 and added strengthening metal, such as chromium or achrome-platinum alloy, i on the flanks of the cutting edge. Such razorblades exhibit excellent shaving characteristics and have a long shavinglife. A wide range of blade substrate materials may be used, specificrazor blade steel compositions with which the invention may be practicedincluding the following:

COMPOSITION IN PERCENT C Cr M0 Si Ni Other objects, features andadvantages of the invention will be seen as the following description ofparticular embodiments progresses, in conjunction with the drawings inwhich:

FIG. 1 is a diagrammatic view of apparatus suitable for practice of theinvention;

FIG. 2 is a diagrammatic view of the geometry of a razor blade edgesharpened by conventional means; and

FIG. 3 is a diagrammatic view illustrating one example of razor bladeedge geometry in accordance with the invention.

DESCRIPTION OF vPARTICULAR EMBODIMENT Diagrammatically shown in FIG. 1is a sputtering apparatus which includes a stainless steel chamber 10having wall structure 12 and a base 14 in which is formed a port 16which is coupled to a suitable vacuum system (not shown). Mounted inchamber 10 is a support 18 on which is disposed a stack of razor blades20 and support structures 22, 24 for target member 26 of dielectricmaterial and target 28 of electrically conductive material. Supportstructures 18, 22 and 24 are electrically isolated from chamber 10 andelectrical connections are provided to connect blade stack 20 andtargets 26, 28 to appropriate energizing apparatus 30, 32, 34. It willbe understood that this is a diagrammatic showing of suitable apparatus.In one embodiment the targets 26, 28 are horizontally disposed discs,each six inches in diameter and one-quarter inch thick; and 4 /z-inchlong stack of blades 20 is placed on a five-inch diameter aluminumsupport disc 18 disposed parallel to target discs 26, 28. Disc 18 ismovable between a first position aligned with target 26 and a sec- 0ndposition aligned with target 28. A coil of razor blade strip may besimilarly positioned on such a support with its sharpened edges defininga plane exposed to parallel to targets 26, 28. In another embodiment,target rod that has an exposed length of twenty-nine inches and is 1%inches in diameter is employed. Suitable coolant is circulated throughthe rod for cooling purposes. A series of stacks of razor blades (eitherin coil form or in twelve inch long axial extending stacks) are disposedabout the target rod at equal distances therefrom.

The geometry of the edge of a typical razor blade of commercial qualitysharpened by conventional abrading techniques is shown in FIG. 2 at amagnification of about 100,000 times. The tip 40 has a radius that istypically in the range of 125-500 Angstroms, a typical average radius(the average of radius measurements taken at 5 to points along thelength of the blade edge) being about 250 Angstroms. The W1 flank width(at a distance of 1,000 Angstroms from the ultimate edge 40) istypically in the range of 1200 to 1400 Angstroms. The W2 width (at adistance of 2,000 Angstroms from the tip 40) is about 2100 Angstroms;the W4 width (at a distance of 4,000 Angstroms from the tip 40) is about3200 Angstroms; and the W6 width (at a distance of 6,000 Angstroms) isabout 4100 Angstroms; and the W8 width (at a distance of 8,000 Angstromsfrom the tip) is about 5100 Angstroms.

These measurements were made by a high resolution electron microscopytechnique in which a magnified image of a blade edge profile(silhouette) is photographed. The blades are cleaned by immersion intrichloroethylene; subjection to ultrasonic cleaning for two minutes;rinsing in a mixture of one-half acetone and one-half methanol; cleanedin warm air; and then demagnetized in a solenoid coil. A blade specimenin the order of one square millimeter in size with four sides, one ofwhich is the original sharpened razor blade edge, is obtained byabruptly snapping the blade with the help of a suitable instrument suchas a watchmakers plier. The blade may be snapped in air or if the bladewill not break readily in liquid nitrogen (at a temperature below theductile to brittle transition value).

A 100 kv. RCA EMU4 electron microscope is used with a standard air lockspecimen holder modified to accommodate the small blade edge fragment.The microscope was fitted with a liquid nitrogen cooled bafile valve toreduce contamination during photography. The blade edge profile is heldin the path of the electron beam so that a shadow image of the ultimatetip is cast on the final viewing screen. The magnification of the finalimage is controlled by the strength of the intermediate lens current andthe focusing is achieved with control of the objective lens current. Themicroscope magnification was calibrated in terms of focusing lenscurrent.

The tip radius of the resulting photomicrograph was measured by fitting90 arcs of circles to the tip profile and selecting as the tip radiusthat edge profile that best fits the profile of the photomicrograph. Thepoint to point resolution of the microscope is in the order of 5Angstroms. The variation and average radius of a large nmnber of edgesfrom a particular batch of blades using this technique was within 12.5Angstroms. The W1, W2 and other dimensions are similarly measured fromthe photomicrograph.

In operation of the apparatus shown in FIG. 1, sharpened blades 20 aredisposed in a stack with their sharpened edges aligned and are placed inchamber 10 on support 18. The chamber is evacuated and the blade edgesare subjected to ion bombardment, for example by a glow dischargemaintained in argon at a pressure of ten microns to modify the edgegeometry as generally indicated by line 42 in FIG. 2 and specifically toreduce the tip radius, a typical radius reduction being about 100Angstroms.

The chamber is again evacuated and argon at a pressure p of 58 micronsis placed in the chamber. With the blade stacks and chamber grounded, anRF potential is applied to dielectric target 26 and argon ions areproduced which bombard target 26 and release atoms of the targetmaterial. The released atoms of dielectric material are deposited onexposed surfaces, including the sharpened blade edges. This layer isapplied uniformly to the thickness of less than 500 Angstroms. Thesupport 18 is then aligned with the target 28 and an RF potentialapplied to that target to cause deposition of an electrically conductivelayer on the dielectric layer. The RF power supply is then disconnectedfrom the target 28 and the blades are subjected to DC ion bombardmentwhich removes electrically conductive but not dielectric material, morematerial being removed from the tip region of the blades than theflanks. The resulting blades have a cutting edge geometry of the naturediagrammatically indicated in FIG. 3 in which the exposed tip 44 isdielectric material and its average radius is about 250 Angstroms andtwo layers 46, 48 are on the flanks at the W6 dimension.

As a specific example, a 4 /2-inch long stack of stainless steel razorblades having the following composition:

Percent Carbon .5462

Chromium 13.5-14.5

Manganese .20.50 Silicon .20.50 Phosphorus, max .025 Sulphur, max. .020Nickel, max .50 max. Iron Remainder sharpened to the edge geometry asindicated in Feb. 2, and sharpened to the edge geometry as indicated inFIG. 2, were placed on a five-inch diameter aluminum disc support 18 inan RF sputtering unit. Two targets were employed, an A1 0 target 26, anda Cr Pt target 28. The A1 0 target 26 was a sintered compact disc sixinches in diameter and inch thick, and the Cr Pt target 28 was a purechromium disc six inches in diameter and A1 inch thick that had squaresof pure platinum foil one centimeter on a side and 0.002 inch thick spotwelded on its surface. The foil squares were spaced on the surface sothat 23% of the chromium surface was covered with platinum. The targetsurfaces were disposed parallel to the sharpened blade edges at adistance of 2 /2 inches from those edges.

Pressure in the vacuum chamber 10 was reduced to 0.1 micron of mercuryand then pure argon gas was bled into the chamber to a pressure of tenmicrons of mercury. The aluminum support disc 18 was then connected to aDC source of power and with the chamber 10 grounded the blade edges weresubjected to ion bombardment at a voltage of 1800 volts and a current of35 milliamperes for seven minutes. The targets 26, 28 were covered bymetal shields during this step. A 13.56 megahertz RF source wasconnected to A1 0 target 26 and that target was sputtered for thirtyminutes while maintaining ten microns of mercury pressure of argon gasin the chamber. The shield was then removed from between the blades 20and the target 26 and 0.4 kilowatts of powder (with a DC negative biasof about 3400 volts and a superimposed RF signal of about 4500 voltspeak to peak) was applied for 10 minutes while maintaining argon at 10micrions pressure. The edges of the blades facing target 26 received analuminum oxide layer 46 to a thickness of about 250 Angstroms.Application of RF power was then terminated and support 18 was alignedwith the Cr Pt target 28. The Cr Pt target 28 was connected to the RFsource and cleaned for five minutes and then a layer 48 ofchromium-platinum alloy 250 Angstroms in thickness was deposited byapplication of 0.4 kilowatts of power for seconds. The blade stack wasthen connected to the DC source and subjected to ion bombardment forseven minutes at 1800 volts at a current of milliamperes to remove thechromium-platinum film from the tip region but not the flank region ofthe blades to provide a blade edge geometry as shown in FIG. 3. Theresulting blades have an average tip radius of 250 Angstroms, an averageW1 dimension of about 1400 Angstroms, aWZ dimension of about 2500Angstroms, a W4 dimension of about 4,000 Angstroms, and a W6 dimensionof about 5150 Angstroms. A coating of polytetrafluoroethylene telomerwas then applied to the edges of the blades in accordance with theteaching in U.S. Pat. 3,518,110. This processing involved heating theblades in an argon environment and provided on cutting edges of therazor blades an adherent coating of solid PTFE. These blades exhibitedexcellent shaving properties and long shaving life.

It will be understood that a variety of dielectric materials includingother metal oxides may be used for the dielectric layer 46 and thatother metals and metal alloys may be used for the electricallyconductive layer 48. Ion bombardment between the application of thedielectric and conductive layers is optional. For example, such ionbombardment may be desirable when the process is employed with separatedeposition chambers with a single target in each chamber.

The invention provides an improved cuting implement such as a razorblade in which the tip radius of the implement is within the optimumrange for cutting effectiveness, the exposed tip is of dielectricmaterial and substantial amounts of edge strengthening materials havebeen added to the flanks of the cutting edge.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention.

What is claimed is:

1. A process for treating a cutting implement comprising the steps offorming a cutting edge in dielectric material on the implement having anaverage tip radius of less than about 500 Angstroms, depositing a layerof electrically conductive material on said dielectric material, saidlayer of electrically conductive material having a total thickness atthe W6 dimension of said cutting implement of at least 100 Angstroms,and subjecting said cutting edge to DC ion bombardment to remove aportion of the deposited electrically conductive material so that saiddielectric material is exposed at the tip of the cutting edge of saidimplement and other portions of the deposit edelectrically conductivematerial remain on the flanks of said cutting edge adjacent said tip.

2. The process as claimed in claim 1 wherein said dielectric material isa metal oxide and said electrically conductive material is metal.

3. The process as claimed in claim 2 wherein said dielectric material isaluminum oxide.

4. The process as claimed in claim 2 wherein said metal includeschromium.

5. The process as claimed in claim 1 wherein said cutting implement is arazor blade.

6. The process as claimed in claim 1 wherein said dielectric materialcutting edge is formed by the steps of forming a cutting edge on a metalsubstrate and then depositing a layer of dielectric material on saidsubstrate cutting edge.

7. The process as claimed in claim 6 wherein said layer of dielectricmaterial is deposited to a total thickness at the W6 dimension of saidcutting implement of at least Angstroms.

8. The process as claimed in claim 6 wherein said dielectric andelectrically conductive materials are deposited by sputtering.

9. The process as claimed in claim 6 and further including the step ofsubjecting said cutting edge on said metal substrate to an initial ionmomlv substrate to an initial ion bombardment step to reduce the averagetip radius of said cutting edge on said metal substrate at least about100 Angstroms, and wherein said dielectric material is deposited to athickness in the range of about 100-300 Angstroms.

10. The process as claimed in claim 6 wherein said dielectric andelectrically conductive strengthening materials are deposited bysputtering techniques on a multiplicity of razor blade elements whilethe blade edges are disposed in parallel alignment with one another andin a plane parallel to a target member spaced from said blade edges.

11. The process as claimed in claim 10 and further in cluding the stepof subjecting said cutting edges to an initial ion bombardment step toreduce the average tip radius of said cutting edges at least about 100Angstroms, and wherein said dielectric material is deposited to athickness in the range of about 100-300 Angstroms.

12. The process as claimed in claim 11 wherein said dielectric materialis a metal oxide and said electrically conductive material is metal.

References Cited UNITED STATES PATENTS 3,345,202 10/1967 Kiss et al74-106 R 2,843,542 7/1958 Callahan 204-192 3,562,140 2/ 1971 Skinner'etal 204-298 3,479,269 11/1969 Byrnes et a1 204-192 3,652,443 3/1972 Fishet al 204-192 3,480,483 11/1969 Wilkinson 204-192 3,682,795 8/ 1972Fischbein et al 204-192 JOHN H. MACK, Primary Examiner S. S. KANTER,Assistant Examiner U.S. Cl. X.R.

nmrnn STATES PATENT oFrrcE QETWKCATE M @QEUHQN Patent No. 3751 7 DatedSeptember 25, 1973 Inventor(s) Aiye swami S. iiastr'i It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 20, delete and--;

Column 4, ,line 28, delete line, beginning with "sharpened" and endingwith "Felon 2,";

Column i, line 56, change powder to "g;ower--; v

Jolumn 5, line 19, change outing" to ---cutting;-;

tolumn 5 lines H t- 15, change deposit delectr'ically to --depositede1ectrically5 Jolumn 6," (Claim 9), delete line 15 starting ,with'"'siaubstrate" and ending with, "momlv".

Signed and sealed this 5th day of March 19714.,

(SEAL) Attest:

EDWARD M F'LETCHERJR, v c. MARSHALL DANN Attesting Officer Commissionerof Patents FORM PC4050 (169) USCOMM-DC scans-pas fi U.5 GOVERNMENTPRINTING OFFICE 2 I955 0-355-334

